In the art of wood and waste combustion systems, a variety of well known techniques and devices are available for heat generation of various kinds. In particular, the wood products manufacturing industry includes combustion techniques and devices which include heat sources for drying equipment. Oftentimes, such combustion techniques and devices are intended to burn all kinds of wood and potentially other solid-carbon-based fuel sources. Such varying fuel sources include waste that is sourced from wood products manufacturing. Not only do the fuel sources vary in composition and physical form, but such fuel sources also vary considerably in terms of moisture content. Accordingly, within this field, there have been many devices seeking to provide improved combustion.
U.S. Pat. No. 2,444,985 discloses a fuel burner for the combustion of solid fuels comprising a blower, a conveyor screw, a cast iron heater surrounded by a sheet metal jacket provided with one or more hot air outlets, cold or return air inlets, a smoke pipe, a furnace base which forms the ash pit, an ash conveyor trough carrying a conveyor screw, refractory walls to enclose a gas chamber, and a burner wherein the usual grates normally provided in the bottom of the heater may be removed or omitted and wherein the inside of the base is lined with a refractory wall forming an interior circular chamber lined with heat refractory material. The burner of this device is installed so that its center axis is offset from the center of the circular chamber.
U.S. Pat. No. 4,074,680 discloses a fireplace structure for burning a combustible fuel comprising an adjustable hood, a stationary smoke pipe, a fire support base, a lowermost base portion for operable mounting of the fireplace base upon a floor surface, a cylindrical support means with a upwardly opening plenum spaced within the fireplace base, a firebrick lining, and a grating means made of a plurality of fire brick laterally and vertically spaced to define updraft air passages for ambient air supplied from a bottom portion of the plenum, wherein the fire brick are laterally and vertically spaced to define updraft passages in addition to supporting any form of combustible material such as coal, wool, charcoal versions of the same, and an ash auger.
U.S. Pat. No. 3,812,794 discloses a combustion furnace having a grate formed as a plurality of downward leading steps from an upper to a lower region with a number of separated, outwardly flaring openings among the steps including a material ram plate, and a stair-step grate formed of a number of refractory bricks which each extend slightly beyond the one above it wherein each of the refractory bricks has a passageway extending through it parallel to the horizontal surface and terminating in an upwardly flaring opening.
U.S. Pat. No. 4,377,117 discloses a furnace for burning dry or wet wood waste products such as hogged bark and the like encompassing a storage bin which contains particulate wood waste material to be burned, a rotary screw conveyor, an intermediate hopper, a rotary feeder, an air flow conduit for a blower, a boiler furnace, a grating structure or grate with spaced-apart support beams having a plurality of parallel rows of bricks positioned thereon with at least some of the rows of bricks maintained a uniform distance from other rows of bricks by spacers, hot air inlet conduits positioned below the grate, and an adjustable intake.
Traditionally, combustion devices have included a fixed grate furnace, though improved versions have displaced the fixed grate types with the walking grate system. This style offers online de-ashing and elevated metal grate bars. The online de-ashing avoids problems associated with a fixed floor furnace, but creates a furnace that cannot burn excessive amounts of dry fuel without the need of wetting the fuel or something similar that drastically complicates the fuel supply arrangement to these combustion devices. In addition, this style of combustion device is typically extremely expensive due to the metal bars in the floor. This is impractical for small wood products manufacturing operations to purchase. Some variations on the fixed grate include a fixed yet sloped floor grate.
While many such solutions exist to the combustion of wood and waste, problems are common to most every configuration of walking grates, fixed floor grates, and fixed floor bins. For example, walking grates do not allow the burning of fuel below 40% moisture content without damaging the metal grates. As well, fixed floor grates often plug and are hard to clean and properly gasify the products of combustion without a mechanically large furnace area. Still further, fixed floor bins are nearly impossible to effectively de-ash while online and prove very difficult to keep air infiltration down.
It is, therefore, desirable to provide improved de-ashing online while improving air distribution around the combustion pile. Moreover, it is desirable to provide a combustion device capable of burning a wide range of fuel moisture contents without the need for modifying the mechanical components of the burner for the given fuel. It is further desirable to enable the combustion of low moisture content fuel without inducing rapid wearing or requiring constant maintenance.